#include <iostream>
#include <Eigen/Dense>

using namespace std;
using Eigen::MatrixXd;

int main()
{
    MatrixXd m(2, 2);
    cout << m << endl;

    m(0, 0) = 3;
    m(1, 0) = 2.5;
    m(0, 1) = -1;
    m(1, 1) = m(1, 0) + m(0, 1);

    cout << m << endl;
    cout << "m is of size " << m.rows() << "x" << m.cols() << std::endl;
}
